A technique by which a transistor is formed using a semiconductor thin film formed over a substrate having an insulating surface has been attracting attention. The transistor is applied to a wide range of semiconductor electronic devices such as an integrated circuit (IC) and an image display device (also simply referred to as display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to the transistor. As another material, an oxide semiconductor has been attracting attention.
For example, Patent Document 1 and Patent Document 2 disclose a technique by which a transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide as an oxide semiconductor and is used as a switching element or the like in a pixel of a display device.
Patent Document 3 discloses a technique by which, in a staggered transistor including an oxide semiconductor, a highly conductive oxide semiconductor containing nitrogen is provided as buffer layers between a source region and a source electrode and between a drain region and a drain electrode, and thereby the contact resistance between the oxide semiconductor and the source electrode and between the oxide semiconductor and the drain electrode is reduced.
Non-Patent Document 1 discloses a top-gate amorphous oxide semiconductor transistor in which a channel region, a source region, and a drain region are formed in a self-aligned manner.